Caffeine Accelerates Absorption and Enhances the Analgesic Effect of Acetaminophen

Abstract

MD, Geoff Clarke, FCB, Tim Grattan, FCB, Angelika Beisel, Christian Mueller, MD, Ulrike Werner, PhD, Gerd Kobal, MD, and Kay Brune, MD A cetaminophen (paracetamol) is a nonopioid, non-NSAID (nonsteroidal anti-inflammatory drug) analgesic that is widely used as an over-the-counter drug for the treatment of mild to moderate pain. The mechanism of action is not yet clarified but may involve inhibition of cerebral prostaglandin synthesis 1-3 and central serotonergic or opioidergic pathways. [4][5][6] Caffeine is a common adjuvant to analgesic drugs. 7,8 The mechanism of its putative analgesia-enhancing effect remains unclear. Caffeine is thought to produce competitive antagonism at adenosine receptors, 9,10 induce changes of the pharmacokinetics of acetaminophen, 11,12 and induce changes in mood, 13 all of which may lead to enhancement of the analgesic action of acetaminophen.The aim of this study was to investigate the analgesic activity of 1000 mg acetaminophen compared with caffeine alone and the combination of both using an experimental human pain model. To define caffeine actions, subjective and objective pain assessments and pharmacokinetic evaluations were included in this study. The pain model used is based on evoked cortical potentials and pain ratings following specific stimulation of nasal nociceptors with gaseous carbon dioxide (CO 2 ), 14,15 and it is also based on pain ratings after tonic painful stimulation of the nasal mucosa with dry air of controlled flow and temperature. 16 This model has been applied successfully to quantify the activity of several nonopioid 15,[17][18][19][20][21][22][23] METHODS SubjectsThe study was approved by the ethics committee of the University of Erlangen-Nuremberg. It was conducted according to the Declaration of Helsinki on biomedical research involving human subjects (Somerset West amendment). Twenty-four subjects were enrolled (12 men, 12 women, aged 18-45 years [median, 26 years]), all within ±20% of their ideal body weight (men: median weight, 75 kg; range, 67-86 kg; women: median weight, 57 kg; range, 51-66 kg). All were found to be healthy by routine clinical examination and laboratory tests at the beginning and end of the study. Oral contraceptives were the only medication allowed during the study. ProtocolThis was a single-center, 4-way crossover, randomized, placebo-controlled, double-blind study. Each subject received a single dose of 1000 mg acetaminophen (Panadol), 130 mg caffeine, 1000 mg acetaminophen plus 130 mg caffeine (Panadol Extra), or placebo, taken with 150 mL of water, after fasting for 6 hours. Subjects remained fasted but were allowed to drink water during the study period. The washout periods between drug administrations were at least 6 days.On each study day, participants were subjected to 5 periods of phasic pain lasting for 20 minutes each and applied at baseline and at 20, 40, 90, and 180 minutes after receiving medication. During a stimulus period, 16 stimuli of 60% v/v CO 2 and 32 stimuli of 70% v/v CO 2 were delivered to the left ...

Multiscale modeling reveals inhibitory and stimulatory effects of caffeine on acetaminophen‐induced toxicity in humans

“…At first, reference PBPK models for APAP and CAF were established by using clinical PK data ( Supplementary Figure S2, Supplementary Table S1‐S5 ) 8, 20, 21, 25. Twenty‐one biochemical processes were implemented in the PBPK models of CAF and APAP ( Figure 2) to represent key metabolic reactions, active drug transport ( Supplementary Table S2 ), as well as elimination processes ( Supplementary Table S4 ) 29, 30…”

“…PICD was applied for a co‐administration of APAP and CAF with a relative dose ratio of 1000:130, according to therapeutic indications 8, 9. When both drugs were given concomitantly, the PICD‐based PD response of APAP ( ${\mathrm{P}\mathrm{D} \mathrm{r}\mathrm{e}\mathrm{s}\mathrm{p}\mathrm{o}\mathrm{n}\mathrm{s}\mathrm{e}}_{\mathrm{D}\mathrm{D}\mathrm{I}}\left(\mathrm{normalA}\mathrm{normalP}\mathrm{normalA}\mathrm{normalP}\right)$) were adjusted according to its changed concentration‐time profile caused by the competitive inhibition of CAF on ABCB1‐mediated and CYP2E1‐mediated transport and metabolization of APAP, respectively 5, 7, 16, 19.…”

“…CAF is often administered as combination therapy in the treatment of pain because CAF is supposed to enhance the analgesic effects evoked by APAP or other analgesic agents 8, 9, 10. In this regard, CAF may alter APAP pharmacokinetic (PK) processes at the organism level8, 11 and may influence APAP‐induced pharmacodynamic (PD) responses at the cellular scale 10. In this context, CAF and APAP may thus be considered as perpetrator and victim drug, respectively 12.…”

“…In such combination therapies, drug‐drug interactions (DDIs) may inevitably occur and may potentially have a substantial impact on the PK behavior and the resulting PD effect of the administered drugs eventually leading to additive, synergistic, or antagonistic drug effects 3, 8, 10, 11, 13…”

“…PD responses of CAF and APAP were therefore predicted for an in vivo situation by the application of PICD14 thereby coupling in vitro toxicity data with drug‐specific PBPK models. To validate the PBPK models, simulated drug concentrations of APAP, CAF, and their main metabolites (APAPC, acetaminophen cysteine; APAPG, acetaminophen glucuronide; APAPS, acetaminophen sulfate; PX, paraxanthine; TP, theophylline; and TB, theobromine) were first assessed with clinical PK profiles from several studies obtained for different dosage regimens 8, 11, 20, 21, 22, 23, 24, 25, 26, 27. Using an additive PD response model, the influence of CAF on APAP‐induced hepatotoxicity was analyzed for key cellular processes and individual genes.…”